1. Field of the Invention
The present invention relates to a photovoltaic power generation system that has an exposed electroactive portion.
2. Related Background Art
In recent years, awareness of ecological problems has been raised worldwide. Among others, the global warming resulting from CO2 emission is a serious concern, and clean energy has been desired increasingly. In such a circumstance, a solar battery shows great promise to serve as a source of clean energy in terms of its safety and operability.
The solar battery includes a photoelectric conversion layer for converting light into electricity, typical materials of which include single-crystal silicon semiconductor, polycrystalline silicon semiconductor, amorphous silicon-based semiconductor, groups III-V compound semiconductor, groups II-VI compound semiconductor and groups I-III-VI2 compound semiconductor.
An example of a typical solar cell module is shown in FIGS. 6A and 6B. In these figures, FIG. 6A is an outside view of a solar cell module 601, and FIG. 6B is a sectional view taken in the line 6Bxe2x80x946B of FIG. 6A. As shown in FIG. 6B, the solar cell module 601 consists of a photovoltaic element 602 that converts received light into electricity, a solar cell envelope, and an output cable 605 for taking out an output, in rough classification. Then, the solar cell envelope comprises a front cover 603 that is made of a glass plate, a light-transmissive resin, or the like and is arranged in the side of a light-receiving surface of a photovoltaic element, a back cover 604 that is made of a glass plate, a resin, a metal plate, or the like and is arranged in the side of a non-light-receiving surface, a frame member 607 to reinforce and fix the solar cell module, and an adhesive 606 to bond the frame member.
In addition, so as to mutually connect solar cell modules in series or parallel, a cable such as an IV wire, a CV cable, or the like that is coated with insulating coating is used.
Then, since a solar cell array that uses these members is strictly given insulation measures to the solar cell modules and wiring members, a DC output generated by the solar cell array hardly flows to the ground as a leakage current Ir even in a moist state like fair weather after rainfall. Therefore, a leakage current from the solar cell array is smaller than a set current of a ground-fault interrupter (earth leakage breaker) in a receiving terminal.
A photovoltaic power generation system utilizing such a solar cell exists in a wide variety of scales from several watts to several thousands kilowatts. For example, a photovoltaic power generation system using a battery to store energy generated by the solar cell, or a photovoltaic power generation system using a DC-AC converter to supply output energy of the solar cell to a commercial electric power system (simply referred to as xe2x80x9csystem (power system)xe2x80x9d hereinafter).
FIG. 2 is a block diagram of a typical photovoltaic power generation system disclosed in Japanese Patent Application Laid-Open No. 2000-207662. In this photovoltaic power generation system, four solar cell strings 204 to 207 are connected in parallel to constitute a solar cell array 201, each of the solar cell strings being composed of a plurality of solar cell modules connected in series. An output of the solar cell array 201 is led to a power conditioner 202 having a controller for controlling a maximum output, for example, and then supplied to a load 203. The load 203 may be a system, and such a system of flowing the power of the solar cell back to the system is referred to as xe2x80x9csystem-interconnecting system (utility connected system)xe2x80x9d.
The typical structure of these system-interconnecting systems will be explained below.
FIG. 4 shows a schematic diagram of a solar cell array that uses a power conditioner without an insulating transformer. Here, reference numeral 401 denotes a solar cell array, 402 does an inverter, 403 does a differential current sensor, 404 does a switchboard, 405 does a system (power system), 406 does a load, 407 does a current I1 that flows from a positive electrode terminal of the solar cell array, 408 does a current I2 that flows into a negative electrode terminal of the solar cell array, and 409 does a ground-fault interrupter.
A DCxe2x80x94DC converter boosts an output from the solar cell array 401, and the inverter 402 converts it into an alternating current at the commercial frequency. In the case of a single-phase three-wire system, electric power is supplied to a 200-V circuit in a single phase, and only a system-interconnecting apparatus detects three lines in a single phase. Since being small, light, and low-cost, and also reliable, this system becomes a main stream in the present power conditioners. Nevertheless, it is known that there is a demerit that, since this system is not isolated from the power conditioner, it is necessary to ground a conductive part of an envelope of a solar battery in preparation for the case where a flaw etc. arises in the envelope of the solar battery, and hence, the construction of the solar cell array becomes complicated.
In this solar cell array without an insulating transformer, it is possible to detect a ground-fault from the solar cell array 401 by the following system.
That is, when the ground-fault arises in the solar cell array 401, a ground-fault current flows in a circuit of (solar cell array)xe2x86x92(ground)xe2x86x92(system (power system))xe2x86x92(power conditioner)xe2x86x92(solar cell array), and hence, the relation between the current 407 and current 408 that are shown in FIG. 4 becomes off balance. The ground-fault can be detected by detecting a differential current between them.
When being connected to the system, these system-interconnecting systems are connected via each receiving terminal. In addition, other loads used are connected in these receiving terminals. FIG. 5 shows the relation between the ground-fault interrupter 409 and load 406 that are installed in the receiving terminal.
The ground-fault interrupter comprises a zero-phase-sequence current transformer 501, a sensitivity-switching device 502, an amplifier 503, a coil 504, an opening and closing mechanism 505, a test button 506, and a leak display panel 507. Reference numeral 508 denotes a system (power system), 509 denotes a load, 510 denotes a power conditioner, and 511 denotes a solar cell array.
The zero-phase-sequence current transformer 501 detects a differential current between an outgoing current from the system side and a returning current from the load. When the leak arises, that is, the differential current is a set current or more, a circuit breaker interrupts a line. In general, in such a ground-fault interrupter, it is possible to set a sensitivity current and detection time with respect to leak.
Then, it is usual that the power conditioner 510 is connected to this load 509 in parallel.
Therefore, as for a set current value of the ground-fault detector incorporated in the power conditioner 510 of the solar cell array using the conventional solar cell module, which is strictly insulated and the wiring members, and a set current value of the ground-fault interrupter installed in the receiving terminal, the set current value of the ground-fault interrupter is set larger than the set current value of the ground-fault detector. This is because it becomes almost meaningless to provide the ground-fault detector since the ground-fault interrupter unintentionally operates before the ground-fault detector operates if the set current value of the ground-fault interrupter is smaller than the set current value of the ground-fault detector.
On one side, in the power conditioners with each insulating transformer, there are two types depending on the type of a transformer.
One type of power conditioner uses a commercial-frequency transformer, and is a system to perform the insulation and voltage conversion with the commercial-frequency transformer after converting a DC output from the solar cell array into a commercial-frequency AC voltage. This system is excellent in thunder resistance and noise cutting property, and can supply electric power to a single-phase three-wire system of distribution line with keeping balance. Nevertheless, since using the commercial-frequency transformer, this system is heavy and expensive.
Another type of power conditioner uses a high-frequency transformer, and is insulated with the small high-frequency transformer after converting a DC output from the solar cell array into a high-frequency AC voltage. After that, the power conditioner converts the high-frequency AC voltage into a DC voltage once, and converts the DC voltage into the commercial-frequency AC voltage again. Since using the high-frequency transformer, this system is small, but has a demerit of being expensive because of complicated circuit structure.
In these insulation transformer systems of photovoltaic power generation systems, since a solar battery and the ground are basically insulated from each other, it is impossible to detect a ground-fault by a method similar to the system without an insulation transformer. Then, in the insulation transformer system of the photovoltaic power generation system, a ground-fault from the solar cell array is detected by the system shown in FIG. 3. Here, reference numeral 301 denotes a solar cell array, 302 does a resistor, 303 does a DC voltage detector, 304 does an insulation transformer, 305 does an inverter, 306 does a switchboard, 307 does a ground-fault interrupter, 308 does a grounding conductor, 309 does a system (power system), and 310 does a load.
Two high-resistance resistors 302 that have the same resistance are connected is series between input terminals of the solar cell array 301, and a node (voltage-dividing point) of both resistors is connected to a terminal of the DC voltage detector 303. The other terminal of the DC voltage detector 303 is connected to the ground through a ground terminal.
Hereafter, a mechanism of ground-fault detection will be explained. Since the DC voltage detector 303 is also a high-resistance body, the solar cell array is electrically connected to the ground through the high-resistance resistor 302 and DC voltage detector 303. When a DC ground-fault does not arise, any current does not flow at both terminals of the DC voltage detector 303, and hence, a voltage to the ground is 0 V. Nevertheless, when the ground-fault to the ground voltage arises, the voltage is generated at both terminals of the DC voltage detector through the leakage current to the ground. Hence, it is possible to measure the presence of the ground-fault by using this.
One of the largest problems of the photovoltaic power generation system is reduction of the power generation cost. Particularly, in order to introduce the photovoltaic power generation system into the electricity market on a full scale, the cost reduction is essential, and it is needed to attain a cost comparing with the cost of conventional thermal power generation or nuclear power generation. However, as reported in an interim report (Jun. 11, 1998) from the Supply and Demand Party of the Advisory Committee for Resources and Energy of the Ministry of Economy, Trade and Industry, the energy cost of the photovoltaic power generation is 2.5 to 6 times the electricity rate in Japan, and a radical cost reduction is needed for full-scale introduction thereof.
In view of such circumstances, the inverters attempted to simplify an environmental resistant coating significantly responsible for a cost of a solar cell module and a disposing member for interconnecting solar cells in series or parallel.
Generally, a cost rate of members of the solar cell module except a solar cell such as a coating member, a frame member, a solar cell envelope such as a junction box and cables, and connectors to the whole solar cell module is near to 50%, which is large. Therefore, if the cost of these members can be reduced, it is possible to expect the remarkable cost reduction of the solar cell module. In addition, by not using the insulating coating material of the cable that connects the solar cell module mutually, it becomes possible not only to reduce material cost, but also to omit the time for peeling the coating material. Hence, there is an advantage that it is possible to reduce the cost of construction such as connection and soldering when constructing the solar cell module.
Then, the present inventors have invented the use of the following solar cell.
That is, though use under an environment from which ordinary people could not go easily in and out was predicated, photovoltaic elements were protected to environmental stress as a requirement specification of the solar cell module, but electric insulation performance was removed from the requirement specification, and a specification that an electroactive portion was partially exposed was examined. As a result, the present inventors found that it was possible to remarkably thin the front cover and the back cover, and hence, it was possible to expect remarkable cost reduction. In addition, the present inventors found that, also as for the connection member that connected the solar cells in series and parallel, similarly, it became possible to expect remarkable cost reduction by removing the insulation performance from the requirement specification.
As shown in FIGS. 6A and 6B, a conventional solar cell module required a lot of materials for an envelope consisting of the front cover 603, the back cover 604, the frame member 607, etc. besides the photovoltaic element 602 that is a component at least necessary for electric power generation. These materials are necessary for protecting the solar cell module from an outdoor environment that receives heat stress, optical stress, and mechanical stress, and for securing electric nonconductivity. Nevertheless, it can be said that these are excessive protection materials when being installed under an environment such as a power generation station which ordinary people cannot go easily in and out, and is strictly controlled with predicating regular maintenance.
Nevertheless, the use of a form of the simplification of environment-resistive coating of the solar cell and/or the use of bare members, which connect solar cells in series and parallel, without the insulating coating caused a problem that a conventional solar cell array had not.
That is, since at least a part of an electroactive portion of the electrode and wiring member of the solar cell, and the series-parallel connection members of the array is bare and is not isolated, a current route is formed in a route of (electroactive portion of solar cell array) to (rain water) to (moist concrete) to (rain water) to (ground) or (electroactive portion of solar cell array)xe2x86x92(rain water)xe2x86x92(ground) when the environment became in a moist state (state that the resistance between the electroactive portion of the solar cell array and the ground decreases by moisture) with rain water etc. As a result, leaks frequently arise from the electroactive portion of the solar cell array to the ground to generate leakage currents unintentionally.
In addition, it was also found that, when an electroactive portion of a solar cell was bare, a leakage current flowing into the ground in a moist state usually exceeded a set current value of the ground-fault interrupter installed in the receiving terminal. (Ir greater than Set current of ground-fault interrupter)
In a power conditioner connected to a solar cell array, if a ground-fault detector operates each time by a leakage current caused in such a moist state, and the system and the array are made to drop out, the power conditioner cannot be used naturally. Then, it is necessary to set the set current value of the ground-fault detector larger than the leakage current in the moist state. This is because it needs much time to maintain the power conditioner whenever a malfunction arises since it is necessary to restore the ground-fault interrupter of the photovoltaic power generation apparatus by a switch in the power conditioner interrupted by the ground-fault detection.
Though it is conceivable to set the set current value of the ground-fault detector not larger than the leakage current and to automatically return the ground-fault interrupter alternatively, the ground-fault detector originally prevents the ground-fault beforehand usually. Hence, since it is dangerous to automatically return this unconditionally, it must not be performed. That is, when the power conditioner is stopped by the ground-fault detector, it is necessary to specify where the ground-fault arises in the solar cell array and to restore the power conditioner after proper treatment is performed. Therefore, this is because an existence value of the ground-fault detector is lost if the power conditioner is automatically returned unconditionally.
However, if the leakage current value in the moist state is larger than the set current value of the ground-fault interrupter like the solar cell whose electroactive portion is bare, the leakage current flows into the receiving terminal with passing through the power conditioner even if the set current value of the ground-fault detector is set larger than the leakage current value. Hence, at this time, the ground-fault interrupter that is installed in the receiving terminal operates unintentionally. As a result, similarly much time is consumed.
In addition, a more serious problem is caused in this case. This is because power supply to all loads, which are connected to the receiving terminal, as well as the photovoltaic power generation system, is interrupted when the ground-fault interrupter that exists in the receiving terminal operates as the result of the occurrence of a leakage current in the solar cell array.
It is not possible to set the set current value of the ground-fault interrupter larger than the above-mentioned leakage current similarly to the ground-fault detector. This is because the set current value is not determined only by the solar cell array since the ground-fault interrupter is different from the ground-fault detector. That is, since the set current value is determined also by demands from other loads, it is dangerous to greatly change this value fruitlessly, and it is also prohibited by the Electrical Installation Standards.
Then, a major object of the present invention is to solve the above-mentioned problems in a photovoltaic power generation system having a solar cell array that has an exposed electroactive portion, separately or in a lump.
The present inventors found that it was suitable to use the following means so as to correspond to the above-mentioned problems. Hereafter, specific means and actions will be explained.
The present invention provides a photovoltaic power generation system comprising: a solar cell array having a plurality of solar cells electrically connected to each other with a wiring member, a power conditioner for converting an output from the solar cell array into AC power, an insulation transformer provided between the solar cell array and a system power supply, a ground-fault interrupter provided between the power conditioner and the system power supply, and a ground-fault detector for detecting ground-fault of the solar cell array, wherein a part of at least any one of an electroactive portion of the above-mentioned plurality of solar cell elements and an electroactive portion of the above-mentioned wiring member is exposed to the outside, wherein a line (electric path) of the above-mentioned solar cell array is grounded, wherein a ground-fault detector is provided at the ground line, and wherein a set current value at which the above-mentioned ground-fault detector judges a ground-fault is larger than a set current value at which the above-mentioned ground-fault interrupter interrupts the line.
When a leakage current Ir [A] flows in a current route from the above-mentioned electroactive portion to the ground, which is formed while the above-mentioned solar cell array operates in a moist state, it is preferable in the photovoltaic power generation system of the present invention that the set current value of the above-mentioned ground detector is larger than Ir, and the set current value of the above-mentioned ground-fault interrupter is smaller than Ir.
In addition, in the photovoltaic power generation system of the present invention, it is preferable that the above-mentioned ground-fault detector operates by using a current flowing in the above-mentioned grounding line as a power supply; that a positive electrode terminal or a negative electrode terminal of the solar cell array is grounded; that a line is ground so that a ratio of an absolute value of a voltage between the positive electrode terminal of the solar cell array and the ground to an absolute value of a voltage between the negative electrode terminal of the solar cell array and the ground may become approximately 2:1; that a part of at least one of an electrode, arranged on the side of a light-receiving surface of the above-mentioned solar cell, and the above-mentioned wiring member is not put in a solar cell envelope; that each of the above-mentioned solar cells comprises a photoelectric conversion layer, a collecting electrode arranged on a side of a light-receiving surface of the photoelectric conversion layer, a surface wiring member and a coating member, and has an exposed portion, which is not coated with the coating member, in a part of the collecting electrode or the surface wiring member; that the above-mentioned coating member is composed of a resin and formed by coating; and that the series-parallel connection member for connecting the above-mentioned solar cells in series and/or parallel is a conductor that is not coated with an insulating material.
In addition, the photovoltaic power generation system of the present invention is characterized in that the above-mentioned solar cell array is installed on a supporting member, and it is preferable in this photovoltaic power generation system that the above-mentioned supporting member is a concrete stand.
As previously stated, in the case of the photovoltaic power generation system connected to a system-interconnecting power conditioner circuit without an insulation transformer, as shown in FIG. 4, since the solar cell array 401 is connected to the grounding line of the system (power system) 405 through an SW element of the system (power system) 405 and the power conditioner, the output of the solar cell array 401 is coupled to the ground while the power conditioner operates. Hence, some voltage is applied between the electroactive portion of the solar cell array 401 and the ground.
In addition, also in the case of the solar cell array connected to the system-interconnecting power conditioner circuit with an insulation transformer, as shown in FIG. 3, the solar cell array is connected to the ground through some extent of a resistance via the ground-fault detector 303. Furthermore, in the United States, as described in IEEE standards 1374-1998: xe2x80x9cGuide for Terrestrial Photovoltaic Power System Safetyxe2x80x9d or National Electrical Code Article 690: xe2x80x9cSolar Photovoltaic Systemsxe2x80x9d, since it is obligated that the line of the solar cell array is grounded somewhere of the line of the array, some extent of voltage is always applied between the electroactive portion of the solar cell array and the grounds.
Therefore, in the solar cell array that has the electroactive portion exposed in a solar cell and/or a wiring member that electrically connects the solar cell, a leakage current route is formed between the ground and the electroactive portion of the solar cell array in a moist state during rainfall or after the rainfall, and a leakage current is generated.
As previously stated, a photovoltaic power generation system using a solar cell array having an electroactive portion in the solar cell and/or the wiring member that is electrically connected to the solar cell frequently malfunctions at a set current value not larger than that of a receiving ground-fault interrupter that is a set current value of a usual ground-fault detector by a leakage current due to a drop of insulation resistance of the solar cell array that is caused by the moist state at the rainfall. Then, it is necessary to set a set current value so that the ground-fault detector should not be dropped at a leakage current that arises in the solar cell array in the moist state.
In a photovoltaic power generation system of the present invention, the sensitivity of a ground-fault detector is dropped (a set current value is made large), and at the same time, so as to prevent a leakage current from flowing into the ground-fault interrupter in a receiving terminal to operate the ground-fault interrupter, an insulation transformer is provided between the solar cell array and the system (power system). Specifically, an apparatus using a high-frequency or a commercial-frequency insulation transformer is used as a power conditioner. As a result, as shown in FIG. 9, since a solar cell array 901 and a system (power system) 907 are insulated by an insulation transformer 902, the circuit of (solar cell array)xe2x86x92(ground)xe2x86x92(system (power system))xe2x86x92(solar cell array) is not connected, and hence, a leakage current never flows into the ground-fault interrupter 905 at the receiving terminal. In FIG. 9, reference numeral 903 denotes a power conditioner, 904 does a switchboard, an 906 does a load.
In this manner, according to the photovoltaic power generation system of the present invention, though the set current value of the ground-fault detector is made larger than the set current value of the ground-fault interrupter, it is possible to prevent the ground-fault interrupter from dropping even if a leakage current of the solar cell array exceeds the set current value of the ground-fault interrupter. Hence, it becomes possible to prevent a malfunction of the photovoltaic power generation system by the leakage current of the solar cell array.
In addition, in the photovoltaic power generation system of the present invention, it is preferable that the above-mentioned ground-fault detector operates by using a current, flowing in the above-mentioned grounded line as a power supply; and that each of the above-mentioned solar cells comprises a photoelectric conversion layer, a collecting electrode, arranged on the side of a light-receiving surface of the photoelectric conversion layer, a surface wiring member and coating material, and has an exposed portion, which is not coated with the coating member, in a part of the collecting electrode or the surface wiring member.